0000000000014265
AUTHOR
Ludwig Schladt
Time-dependence and differential induction of rat and guinea pig peroxisomal beta-oxidation, palmitoyl-CoA hydrolase, cytosolic and microsomal epoxide hydrolase after treatment with hypolipidemic drugs.
Fischer-344 rats and Hartley guinea pigs received a diet containing 0.01% (w/w), 0.05% (w/w), or 0.25% (w/w) of the hypolipidemic drug fenofibrate. Rats were treated for 4, 7, 14, or 21 days, and a clear dose-dependent and weak time-dependent increase in liver/body weight ratio was observed. The specific activity of peroxisomal beta-oxidation increased linearly with time at all concentrations used. A dose-dependent increase in cEH was observed, but the activity remained constant after treatment for 7 days. Enhancement of palmitoyl-CoA hydrolase was dose-dependent, but was similar at all 4 time points investigated. In contrast to the other enzyme activities, mEH was not or only minimally (le…
Rat and human liver cytosolic epoxide hydrolases: evidence for multiple forms at level of protein and mRNA.
Two forms of human liver cytosolic epoxide hydrolase (cEH) with diagnostic substrate specificity for trans-stilbene oxide (cEHTSO) and cis-stilbene oxide (cEHCSO) have been identified, and cEHCSO was purified to apparent homogeneity. The enzyme had a monomer molecular weight of 49 kDa and an isoelectric point of 9.2. Pure cEHCSO hydrolyzed CSO at a rate of 145 nmole/min/mg. TSO was not metabolized at a detectable level, and like cEHTSO, the enzyme was about three times more active at pH 7.4 than at pH 9.0. Unlike cEHTSO, cEHCSO was efficiently inhibited by 1 mM 1-trichloropropene oxide (90.5%) and 1 mM STO (92%). Similarly, liver cEH purified 541-fold from fenofibrate induced Fischer 344 ra…
Microsomal and cytosolic epoxide hydrolases, the peroxisomal fatty acid beta-oxidation system and catalase. Activities, distribution and induction in rat liver parenchymal and non-parenchymal cells.
A number of structurally unrelated hypolipidaemic agents and certain phthalate-ester plasticizers induce hepatomegaly and proliferation of peroxisomes in rodent liver, but there is relatively limited data regarding the specific effects of these drugs on liver non-parenchymal cells. In the present study, liver parenchymal, Kupffer and endothelial cells from untreated and fenofibrate-fed rats were isolated and the activities of two enzymes associated with peroxisomes (catalase and the peroxisomal fatty acid beta-oxidation system) as well as cytosolic and microsomal epoxide hydrolase were measured. Microsomal epoxide hydrolase, cytosolic epoxide hydrolase and catalase activities were 7-12-fold…
Rat Cytosolic Epoxide Hydrolase
Rat liver microsomal and cytosolic epoxide hydrolase may be distinguished through differences in substrate specificity: styrene 7,8-oxide is preferentially hydrolyzed by the microsomal form, while trans-stilbene oxide is the prefered substrate for cytosolic epoxide hydrolase. Large interindividual differences in the specific activity of SpragueDawley (outbred strain) liver cytosolic epoxide hydrolase were observed, varying from 2 to 77 pmol/min x mg protein. Interindividual variations were much lower for microsomal epoxide hydrolase. The specific activity of Fischer F-344 (inbred strain) liver cytosolic epoxide hydrolase varied only by a factor of 2. The specific activity of cytosolic epoxi…
Human liver cytosolic epoxide hydrolases.
Human liver epoxide hydrolases were characterized by several criteria and a cytosolic cis-stilbene oxide hydrolase (cEHcso) was purified to apparent homogeneity. Styrene oxide and five phenylmethyloxiranes were tested as substrates for human liver epoxide hydrolases. With microsomes activity was highest with trans-2-methylstyrene oxide, followed by styrene 7, 8-oxide, cis-2-With methylstyrene oxide, cis-1,2-dimethylstyrene oxide, trans-1, 2-dimethylstyrene oxide and 2, 2-dimethylstyrene oxide. With cytosol the same order was obtained for the first three substrates, whereas activity with 2, 2-dimethylstyrene oxide was higher than with cis-1,2-dimethylstyrene oxide and no hydrolysis occurred …
Epoxide Hydrolase Isoenzymes and their Individual Contribution to the Control of Toxic Metabolites
Epoxides are highly strained three membered cyclic ethers which are formed in vivo by the microsomal cytochrome P450 dependent monooxygenases as intermediates of several important biosynthetic pathways (leukotriene A4, squalene 2, 3-oxide) and as metabolites of numerous xenobiotic compounds containing olefinic or aromatic double bonds. Further transformation of these epoxides may occur by either, rearrangement to phenols, aliphatic aldehydes, or ketones; by cytochrome P450 dependent reduction to the parent compound; or by spontaneous or enzymatic conjugation to gluta-thione. Epoxides may also bind covalently to cellular nucleophiles, such as proteins and nucleic acids thus eliciting carcino…
Purification and characterization of rat-liver cytosolic epoxide hydrolase.
Rat liver cytosolic epoxide hydrolase has been purified and characterized. The enzyme was purified from tiadenol-induced rat liver 540-fold with respect to trans-stilbene oxide as a substrate. Similar purification was obtained with the substrates trans-beta-ethyl styrene oxide and styrene 7,8-oxide, the specific activities decreasing in the order trans-beta-ethyl styrene oxide greater than styrene 7,8-oxide greater than trans-stilbene oxide. The enzyme exerts highest activity at pH 7.4 Km and Vmax of the pure enzyme for trans-stilbene oxide were 1.7 microM and 205 nmol x min-1 x mg protein-1 respectively. With trans-stilbene oxide as a substrate, the inhibition by organic solvents (2.5% by …
The distribution, induction and isoenzyme profile of glutathione S-transferase and glutathione peroxidase in isolated rat liver parenchymal, Kupffer and endothelial cells.
The distribution and inducibility of cytosolic glutathione S-transferase (EC 2.5.1.18) and glutathione peroxidase (EC 1.11.1.19) activities in rat liver parenchymal, Kupffer and endothelial cells were studied. In untreated rats glutathione S-transferase activity with 1-chloro-2,4-dinitrobenzene and 4-hydroxynon-2-trans-enal as substrates was 1.7-2.2-fold higher in parenchymal cells than in Kupffer and endothelial cells, whereas total, selenium-dependent and non-selenium-dependent glutathione peroxidase activities were similar in all three cell types. Glutathione S-transferase isoenzymes in parenchymal and non-parenchymal cells isolated from untreated rats were separated by chromatofocusing …